Document WO 2008/146290 A2 describes a light source device comprising at least one light emitting element, an optical funnel for distributing light emitted by the light emitting element into a waveguide material which is in optical communication with the optical funnel and at least one reflector contacting the waveguide material for redirecting light back into the waveguide material such as to reduce illumination exiting the waveguide material in any direction other than a circumferential direction.
Different colors can be produced with a color variable lamp where phosphor is stacked on top of at least two chips emitting at two different wavelengths. The phosphor is chosen in such a way that it absorbs light differently at different wavelengths. However, two or more chips placed next to each other are required in order to increase the emission area. Furthermore, different colors are produced next to each other rather than on top of each other and due to the overlap in the absorption spectra of phosphors it is difficult to produce saturated colors.